Apparatus for the continuous casting of tubular products



B. TARMANN Sept, 16, 1969 APPARATUS FOR THE CONTINUOUS CASTING OF TUBULAR PRODUCTS Original Filed Jan. 8. 1965 FIG? United States Patent O U.S. Cl. 164-282 3 Claims ABSTRACT OF THE DISCLOSURE Apparatus for continuously casting hollow high melting point metal tubes comprising a generally vertical mold having an open top and bottom. Means for feeding the molten metal into the top of the mold are provided above the mold, and driven as well as non-driven rollers are positioned below the mold to receive and guide the casting. As the casting emerges from the mold it has a solidified skin and a liquid core. The rollers guide the casting along a curved path having a descending initial portion and an ascending succeeding portion. Means (cutting means or plugging means) are provided along the ascending portion of the path to insure a barometric equilibrium between the pressure on the molten metal in the mold and the liquid core in the casting so as to maintain the height of the liquid-gas interface at the top of the liquid core.

This is a division of Ser. No. 424,297, iiled Ian. 8, 1965, which has now matured into Patent No. 3,346,036.

Since the time when a continuous casting of highmelting alloys, particularly of iron and steel, was feasible, there have been numerous suggestions and attempts to also make tubular castings in this manner. Usually, the liquid metal was poured into the annular space between a water-cooled mold for continuous casting and watercooled core, and the tubular casting was continuously lowered from the mold, possibly in a partially solidified state. Owing to the relationships between various factors, such as pouring rate, pouring temperature, taper of the mold and of the core, cooling effect of the mold and core,

properties of various alloys, etc., this casting process can,

be performed only with great diiculty so that it has not found widespread application.

It is an object of the invention to eliminate the disadvantages of the known processes and provide a process which can be carried out on a commercial scale. To accomplish these objects, the invention provides a process for the continuous casting of tubular products, particularly tube blanks, in which, just as in the casting of solid products, molten material is poured in known manner into the top end of an open-ended mold for continuous casting and the partially solidified casting withdrawn from such mold is guided along an initially descending and then ascending, curved path to a level at which the liquid part of the casting cannot rise further. This liquid metal inside the casting rises only to that level as pouring and withdrawing of the casting is continued, whereas the casting drawn beyond said level is hollow.

Because the process according to the invention does not use a water-cooled mold core for shaping the cavity of the casting, all disadvantages previously caused by such a water cooled core are eliminated. In addition, all means for holding, moving and cooling the mold core are eliminated so that the casting equipment is greatly simplilied. Known means, which have proved satisfactory for casting solid products and are reliable in operation, may be used for charging and distributing the metal. The conveyance and cooling of the casting when it has left the mold may also be carried out as in the case of solid castings. The casting, however, is not guided along a curved path only to the level of the mold outlet and then straightened, as is known, but its movement along a curved path is continued, e.g., to the level of liquid metal in the mold. At this level, the pressure on the liquid core of the casting is just as great as the pressure of the surrounding atmosphere providing the surface of the liquid metal in the mold is also subjected to atmospheric pressure. If an opening is provided in the solidified skinl of the casting at this level, e.g., by means of a cutting torch, and the starting end or plug is entirely severed, the curved casting will form an approximately U-shaped vessel having communicating limbs. In the interior of the casting, the melt extends from the level of the surface of the molten metal in the mold to the same horizontal level in curved casting. That portion of the casting which rises above this liquid level is hollow and may be bent into a horizontal direction or may be cut into the desired lengths while moving further along an ascending path.

On the other hand, if the surface of the molten metal in the mold is not subjected to the normal atmospheric pressure but to a higher or lower pressure, the lowest level on which the casting can be cut open without risk of an outliow of liquid metal will be shifted downwardly or upwardly, depending on the pressure conditions.

According to the invention, hollow bodies may also be made without opening the skin of the casting. In this case, the casting must be moved along the ascending path at least to that level in which a vacuum will be formed inside the casting. This level will depend on the pressure conditions and is about 1.40 meters above the horizontal surface of the molten metal in the mold if this surface is subjected to normal atmospheric pressure. Lowering the atmospheric pressure on this surface will lower the liquid level in the casting toward that of the surface of molten metal in the mold.

Compared to the continuous casting of tubular products with the aid of a cooled mold core, the tubular products made according to the invention have an impervious wall. This advantage can easily be understood because it is known that porous portions or voids formed during the solidiiication of melts are mainly formed where solidiiication fronts meet. According to the invention, however,

there is only one solidiiication front, which shifted from the exterior surface of the casting in an inward direction and from the upper end of the melt in the ascending limb f and forms the inside surface of the hollow casting. In

casting tests, it has been found that the inside surface of the tubular casting formed in this manner is surprisingly smooth so that the tubular castings obtained by the invention are highly suitable for being processed into seamless tubes.

The process according to the invention is preferably carried out with the aid of an arcuate mold, which is left by the casting in a curved form so that the initially thin and sensitive skin of the casting is not subjected to bending stress. In this case that arc of the casting which is below the surface of the molten metal in the mold may be particularly short so that tubular castings having a small wall thickness may be made.

For instance, a tubular casting may be made according to the invention as follows: liquid steel is charged into a water-cooled mold for continuous casting in known manner from a conventional ladle with the aid of an offset tundish. The mold cavity has a circular crosssection and is curved according to an arc of a circle, the axis of the mold cavity forming a part of a circle. Only a part of the casting is solidified in the mold so that the casting which emerges from the mold and is shaped according to an arc of a circle has a liquid core. In close succession to the mold, the casting is moved along a path which is also arcuate or circular to the level of the top of the mold by means of guide rollers, at least some of which are driven. During this movement, the casting is cooled further by sprayed cooling water so that its solidified skin increases in thickness. As soon as the starting end of the casting has reached said level, the cold starter bar or plug is severed and an opening is formed in the skin of the casting by a torch approximately on the level where the liquid core of the casting begins. The casting emerging upwardly from the guide path is straightened by a multi-roller straightener and is then cut with cutting torches to the desired length. When the casting process is terminated, the withdrawal of the casting must be interrupted until the casting has completely solidified because liquid steel would otherwise liow about the equipment. Hence, the last portion of the casting is not hollow. A tubular casting made in this manner from steel containing, e.g., 1% carbon and 1.5% chromium has an outside diameter of about 150 mm. and an inside diameter of about 50 mm. when the mold cavity is 150 mm. in diameter, the radius of the curved axis of the mold cavity and of the curved guide means for the castings is 1.5 meters, and the pouring and withdrawing speed is 1.5 meters per minute, cooling water being used at the same rate as with solid castings.

To make tubular castings having a larger wall thickness, molds having a straight axis may be used and the casting may be guided along a curve (for instance of circular or parabolic shape) only from a point spaced below the mold with the aid of guide rollers. In any case, the liquid core in the casting must have a liquid top surface exposed to the interior of the tubular casting.

According to the invention, the wal-l thickness of the tubular casting to be made is controlled by a suitable design of the curved path for the casting below the level of the melt in the mold and by a control of the pouring speed and/or of the direct water cooling. In making tubular castings having a particularly small wall thickness, it may even be necessary to cool only a short portion of the casting emergingfrom the mold with sprayed water and to provide a suitable heat insulation for the casting in the remainder of the curved path traversed by the casting having a liquid core, in order to inhibit a further dissipation of heat.

The uniformity of the wall thickness and the quality of the inside surface of the tubular castings made according to the invention may be improved by the action of electromagnetic fields or of vibrators on the liquid core of the casting so as to agitate this liquid core and ensure an equalization of temperature.

The invention may be applied to special advantage to circular or square cross-sections.

Two embodiments of the invention are shown by way of example in FIGS. l and 2, respectively, both figures being diagrammatic vertical sectional views, and in which like reference numerals refer to analogous parts.

In both embodiments, molten steel is discharged from a ladle 1 into an offset tundish 2, from which the melt is poured into the top end of a water-cooled mold 3 for continuous casting. This mold extends generally vertical and has open top and bottom ends. The casting 5 emerging from the bottom end of the mold has a solidified skin and a 'liquid core. This casting is positively fed and guided along an arcuate path having a descending initial portions and an ascending succeeding portion by guiding rollers 4, which engage opposite sides of the casting. At

.least part of said guiding rollers 4 are driven feeding rollers, which serve to advance the casting along the curved path.

The ascending portion of the curved path defined by the guiding rollers 4 extends above the level of the top surface 7 of the liquid core of the casting 5 in the ascending portion of the curved path. Above this level, a torch 6 may be applied to form an opening through the skin of the casting 5. Through this opening, the interior of the hollow casting above the liquid-'gas interface 7 at the top of the liquid core communicates with the outside atmosphere and barometric equilibrium is maintained. This top surface of the liquid core is on the same horizontal level as the top surface of the molten material in the mold 3.

The guiding rollers 4 are arranged to feed the casting 5 as a hollow casting beyond the interface 7.

The two embodiments differ in that in FIG. 1 the axis of the mold 3 is curved according to an arc of a circle and the guidingrollers 4 are arranged so that the axis of the casting 5 guided by said rollers along the curved path follows an arc of the same circle as the axis of the mold.

In FIG. 2, the axis of the mold 3 is straight and the guiding rollers 4 are arranged to deflect the casting 5 gradually from the direction of the axis of the mold 3 into the curved path.

What is claimed is:

1. Apparatus for the continuous casting of hollow high melting point metal products comprising a generally vertical mold for continuous casting, said mold having open top and bottom ends; means for feeding molten metal into the top of said mold; means for receiving from the bottom end of said mold a continuous castingV having a solidified skin and a liquid core; means for positively feeding and guiding said casting along a curved path having a descending initial portion and an ascending succeeding portion; and means for ensuring a barometric equilibrium between the pressure on the molten metal in the mold and that on the liquid core in said casting while the casting is guided along said curved path so as to maintain the height of the liquid-gas interface at the top of said liquid core in said ascending portion of said curved path, thereby forming said hollow product.

2. Apparatus as claimed in claim 1 wherein said means for receiving, positively feedingr and guiding said casting comprises a plurality of feeding and guiding rollers adapted to engage the outside of said skin at points spaced along said path.

3. Apparatus as claimed in claim 1 wherein said barometric equilibrium ensuring means comprises means for cutting through the skin of the ascending casting at a level above the level of the liquid metal in said mold so that atmospheric pressure will main the height of said interface.

References Cited UNITED STATES PATENTS 3,287,773 11/1966 Woodbury 164-82 X FOREIGN PATENTS 123,117 12/ 1946 Australia.

OTHER REFERENCES Scientific American, The Continuous Casting of Steel, vol. 209 No. 6, December 1963, Tl. S5, pp. 86-88.

J. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner 

